Process control systems, such as distributed or scalable process control systems like those used in chemical, petroleum, power, pulp and paper, or other processes, may include one or more pipes to facilitate movement of a fluid throughout the process plant. In some applications, steam or another fluid may be transported through the process plant and superheated and cooled at prescribed locations within the system. For example, an attemperator or desuperheater may be utilized to cool the steam within a steam pipe assembly between superheating stages in a boiler or in a heat recovery steam generator. The steam pipe assembly may include a liner pipe disposed within a main pressure boundary pipe to protect the boundary pipe from the cooling liquid that is sprayed into the steam pipe assembly to cool the steam. The liner pipe decreases the likelihood of the boundary pipe cracking due to the thermal shock or thermal quenching that may occur during the injection of the cooler liquid into the flow of steam.
Many pipe assembly configurations that include a liner pipe within a boundary pipe or an outer pipe involve the use of alignment rods positioned between the outside of the liner piper and the inside of the boundary pipe. The alignment rods may be welded to the outside of the liner pipe and generally prevent the liner pipe from vibrating within the boundary pipe. When the shape of the liner pipe and/or the boundary pipe is irregular or not compatible for fitting together, it can be difficult to place the liner pipe with the attached alignment rods within the boundary pipe. To accommodate the placement of the liner pipe within the steam pipe assembly, it is common to machine-bore the entire interior of the boundary pipe and/or machine down portions of the alignment rods.